"Oh, Chow! What would we ever do without you?" Sandy said, and the cook beamed. Suddenly, in the midst of the lively chatter and laughter, the dance floor was plunged into total darkness! Phyl clung fearfully to her escort. "Tom!" she gasped. "This is another trick of your enemy's to harm you!" CHAPTER XII DETECTION TEST "Don't worry, Phyl. It may be only a blown fuse," Tom tried to assure the fearful girl. But Tom was worried himself. Not only might he be in danger, but it could involve his friends! Nevertheless, he raised his voice above the excited babble. "Please be calm, everyone! We'll have the lights on again in a jiffy!" Taking Phyl by the hand, Tom groped his way toward the main door. "Let's check the switch," he murmured, and ran his hand over the wall near the door. He located the metal plate and flipped the switch. The lights went on! Good-natured cheers arose. Bud, grinning but puzzled, left Sandy's side long enough to come over and speak to Tom. "What happened?" "I guess some practical joker clicked off the switch." Bud suddenly caught sight of a stout youth in a plaid shirt and blue jeans, who was standing in a nearby corner. He was shaking all over with half-stifled merriment. "There's the wise guy! Rock Harriman!" Rock, an all-star tackle on the Shopton High football team, was well known for his pranks and practical jokes. Bud rushed over. "Okay! Confess!" the husky young flier roared in a jokingly ferocious tone. "Don't get sore!" Rock gasped between chuckles. "I couldn't resist. Boy, did you hear everyone squeal when the lights went out?" Tom grinned in relief. "How about another dance, Phyl?" As the music struck up again, he squeezed Phyl's hand. "I sure appreciate your concern, even if I didn't rate it." Phyl blushed as she returned the squeeze. "You rate with me," she confided shyly. The festivities finally ended after a thoroughly enjoyable evening. Both Sandy and Phyl declared to their dates that it more than made up for the forgotten beach party. "But let's not wait too long for the next date," Sandy warned playfully. "Okay, that's a deal," Bud promised. The next morning at the plant Tom called on Harlan Ames. He told of the sinister hoax by the caller who had passed himself off as Lester Morris. The security chief promised to investigate. "I'll tip off the police about Len Unger," Ames added. "If they can find him, we may be able to crack this case wide open." Tom telephoned Bud, Hank Sterling, and Arv Hanson to meet him at the helijet hangar. The four took off in one of the Swifts' Whirling Ducks, which was standing by loaded and ready. Soon they landed on Fearing Island, where Tom would try out his antidetection invention. "What'll we use for a test sub, skipper?" Hank asked as they drove toward the docks. "A jetmarine," Tom replied. A truck with engineers and technicians was following the jeep. It carried the equipment which Tom and Bud had assembled the previous day.